I Think that w3schools is very good for all languages but wait for other opinion
There's a book from the "The Hard Way" series, which I really like. Too bad it only has until Chapter 15 (out of 32 planned).
This is a good course, and it's page is interactive, meaning you can try out the comands they're teaching you right there (pretty much like Codecademy).
As S1M046 mentioned, w3schools is good for learning. I learned from there when a job I was applying required it (and I knew nothing about it, learner enough to make queries and simple modifications of databases in less than 3 days).
Maybe you should learn how to post in Null-Byte first...
Have you search the forum?
it depends on which one you want to learn , sql is the standard one , for example : MSSQL (microsoft Sql) is a dialect of the standard sql .
which sql helps better for sql injection